Scientific Programme
Biomechanics & Motor control
IS-BM04 - Neural modules in the control of movement: assessing the utility of EMG recordings
Date: 02.07.2025, Time: 14:45 - 16:00, Session Room: Castello 1
Description
As a measure of muscle activation, electromyographic (EMG) recordings comprise the sum of muscle fiber action potentials. These signals are most often obtained from electrodes that are attached to the skin over a muscle of interest. Such recordings, however, provide limited information about the underlying strategies used by the nervous system to perform various actions. More detailed information can be obtained from recordings of motor unit action potentials, the sum of which represents the neural drive sent from the spinal cord to the involved muscles to perform an intended action. The purpose of this symposium is to examine contemporary approaches used to decode the neural strategy embedded in EMG recordings. To achieve this goal, the three presenters will describe a new technology that can obtain more complete recordings of motor unit action potentials (Associate Prof. Muceli), discuss the neuromuscular structure and function of the hamstring muscles (Mr. Sahinis), and share recent findings on neural modules at the motor unit level (Prof. Enoka).
Chair(s)
Roger Enoka
University of Colorado, Boulder, Integrative Physiology
United States
Speaker A
Silvia Muceli
Chalmers University of Technology, Electrical Engineering
Sweden
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High-density intramuscular electrode arrays
Although the concurrent activity of multiple motor units can be recorded with grid electrodes attached to the skin over a selected muscle, these recordings are limited to superficial muscles and are easily contaminated by crosstalk. More selective recordings can be obtained with intramuscular electrodes that can be inserted into both superficial and deep muscles. Importantly, relatively recent advances in technology have included the development of intramuscular electrodes with multiple detection points, so-called high-density intramuscular electrodes. These electrodes allow the simultaneous and accurate detection of large populations of motor units providing insight into mechanisms of human movement. Remarkably, the availability of multiple intramuscular EMG channels enables highly accurate automatic decomposition into the trains of motor unit action potentials activating a muscle compared with the decomposition of single channel EMG that requires considerable interaction by the human operator. We have used this technology in multiple experiments in humans and different animal species to investigate neural connectivity among trains of motor unit action potentials, compartmentalized activation of muscles, force estimation, responses to postural changes, and changes in motor unit composition following transfer of motor axons. The talk will focus on applications in the field of motor control and touch upon technological developments.
Speaker B
Chrysostomos Sahinis
Aristotle University of Thessaloniki, School of Physical Education & Sport Science at Serres
Greece
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Neuromuscular characteristics of individual hamstring muscles
The anatomy, mechanical properties, and relative contributions to the net hip extensor and knee flexor torques differ across the four hamstring muscles (semitendinosus, semimembranosus, and the long and short heads of biceps femoris). Pennation angle, for example, is greatest in the long head of biceps femoris and least in semitendinosus, which maximizes force capacity and range of motion, respectively, in the two muscles. Moreover, the force produced by the long head of biceps femoris varies with changes in hip and knee angles, whereas the torque produced by semitendinosus does not. The anatomy of semitendinosus differs from the other hamstring muscles by the presence of a tendinous inscription in its middle to which the muscle fascicles in the proximal and distal compartments attach. Moreover, each compartment is innervated by a separate branch of the tibial nerve. As a result of this anatomy, the neural drive to the two compartments during submaximal isometric contractions is independent, as indicated the low correlations in the neural drive to the two compartments as measured with high-density surface EMG electrodes. Although the overall activation of biceps femoris and semitendinosus does not differ across exercises, some exercises preferentially engage one muscle over the other. For example, hip-dominant exercises primarily engage the semitendinosus. Recent advances in high-density surface EMG have been used to acquire a more detailed assessment of muscle activation patterns and neural drive to the hamstring muscles during different exercises. Integrating these advanced techniques can enhance our understanding of hamstring function, with significant implications for improving injury prevention strategies, optimizing rehabilitation protocols, and augmenting athletic performance.
Speaker C
Roger Enoka
University of Colorado, Boulder, Integrative Physiology
United States
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Neural modules at the motor unit level
In the field of motor control, the term “synergy” is used to denote a motor module developed by the nervous system to manage the redundant degrees of freedom that are available to perform an intended action. Motor modules derived from covariation in the amplitudes of surface EMG recordings are known as “muscle synergies”. They are presumed to reflect the concurrent activation of several muscles by the same motor command. Neural modules can also be defined at the motor unit level by using factor analysis to identify motor units with correlated modulation of discharge rates. This approach requires the use of high-density EMG technology to record the activity of many motor units in several muscles. Motor units with correlated discharge rates are presumed to share a significant proportion of synaptic input. These neural modules are referred to as “motor unit modes”. In contrast to the extensive literature on muscle synergies, recent findings indicate that not all the motor units in a muscle belong to the same motor unit mode. This means that the shared synaptic input is distributed to sets of motor units within and across muscles. Moreover, the strength of the correlated discharge rate among the motor units within a mode can be changed by a brief bout of physical activity. These findings provide new opportunities to explore the plasticity of networks within the spinal cord of humans.